Step 1th, open the Word2010 document window, click the formula you want to add the letter notation to so that it is edited, and position the insertion cursor in the target location, as shown in Figure 1.
Figure 1 Click the formula that you want to add the letter-class symbol to
Step 2nd, click the other button in the symbol group in the formula Tools/design ribbon to open the symbol panel, and then click the Drop-down triangle button at the top. Select the alphabetic Symbols option in the Open Drop-down menu and select the desired letter symbol in the open letter Symbols panel, as shown in Figure 2.
Figure 2 Choosing to add the letter class symbol